Weighting separated objects as one
This problem is nicely solvable with voxel binding that unfortunately blender doesn't have yet.

The problem would be less visible if the polygons would be segmented the same on the torso and the belts, increasing the polycount will help against the artifacts.

A blender solution is to join everything into 1 piece mesh:


with boolean union and clean up the mesh after it
with knife tool to cut slots for the belts in torso and to cut out excess belts inside the torso. Then joining it together.